A storage system can retain persistent point in time data to enable the quick recovery of data after data has perhaps been corrupted, lost, or altered. For example, a user accessing a document file may alter the document, save the document file, and later have remorse that the document should not have been altered. To recover the unaltered document, the user may access or be given access to persistent point in time data of the unaltered document by a storage system, administrator. Exemplary persistent point in time data is stored in a Snapshot™, available in technology offered by Network Appliance Inc., of Sunnyvale Calif.
When transferring logically organized data between two storage systems, such as data logically organized in volumes, persistent point in time data and current versions of the data can be transferred between the storage systems. However, during the transfer of volumes between the storage systems, transferring all persistent point in time data may increase the time to perform the data migration, thus causing one or both of the storage systems to be unavailable for user access. Further, data migration of volumes between multiple storage systems may cause more than two systems to be unavailable.
A solution to increase the availability of the storage systems during data migration is to transfer a portion of the persistent point in time data, thus reducing the time users have no access to the storage systems. However, this is not an optimal solution because persistent point in time data that are not migrated may be needed. For example, if the migrated current versions of the data and the migrated persistent point in time data do not contain the unaltered data sought by a user, then the user may become dissatisfied.
Accordingly, what is needed is a method and system to provide high availability of storage systems during data migration while retaining all persistent point in time data.